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Username Post: Do I need to use Residual Pressure Valves on my brakes?        (Topic#220623)
Charlie57 
Valued Contributor
Posts: 3000
Charlie57
Loc: Lebanon, Tennessee
Reg: 03-30-08
07-03-09 07:14 PM - Post#1728576    

I only learned about these when I saw them in the Speedway Catalog. They show them used in a typical setup. According to them I would use a Proportioning valve and two residual pressure valve, one for the front and one for the rear. Do I need these? I am planing to buy the Non Adjustable Proportioning Valve for my 4 wheel disc brake set up or do I need to buy an adjustable style?

Charlie



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awsum55 
Senior Member
Posts: 8838
awsum55
Age: 62
Loc: O.P. Kansas
Reg: 09-27-01
07-03-09 09:51 PM - Post#1728656    
    In response to Charlie57

You will not need residual valves for a disk brake set up unless your master cylinder is below your bleeders on the calipers. Like under the floor.

Residual valves are used to keep the brake shoes close to the drums on a drum brake set-up.

As far as the proportioning valve, I don't think you will need one of those either. I've read that if you use the right MC and calipers to match, you won't have any rear lock-up problems.
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4dr 57 
"6th Year" Silver Supporting Member
Posts: 3389
4dr 57
Loc: The Texas Hill Country
Reg: 11-10-04
07-03-09 10:03 PM - Post#1728661    
    In response to Charlie57

The the purplish residual valve pictured when used on a tri5 is usually used in conjunction with a Disc/Drum set up because of the volume differential needed between the 2 types of brakes.
The brass type of Prop valve pictured could be used for the same purpose and should be used with the matching master cylinder. In your case, from an all disc brake setup, like some 80's corvettes. With an all Disc system,useing an all wheel disc brake master cylinder should be used for best efficiency. Your car will probably have a different weight bias then the vehicle the MC/Prop Valve was originally used on, so I am not exactly sure if it's applicable to your situation.

On your all disc brake system an adjustible PV should really fine tune the brakes because the volume requirements are equal all the way around and the only thing you may have to adjust for is the weight differential. Cool.
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MikeB 
Senior Member
Posts: 9479
MikeB
Loc: Plano, TX
Reg: 08-28-03
07-04-09 05:01 AM - Post#1728754    
    In response to awsum55

  • awsum55 Said:
You will not need residual valves for a disk brake set up unless your master cylinder is below your bleeders on the calipers. Like under the floor.


However, some vendors say you should use a 10 psi valve for rear drums even if the M/C is on the firewall, as well as a 2 psi valve for front discs. The idea is to keep a little pressure on them so the pedal doesn't have to travel as far when you step on the brakes. That said, I personally don't know if you can even notice the difference.

As for the prop valve, my understanding is its mission in life is to keep the rear brakes from locking up before the fronts under heavy braking. These are absolutely required in pickups, especially those with a long wheelbase, which tend to have very little weight over the rear when unloaded.

If your car does need a prop valve, I agree you should use an adjustable one in the rear line.

Real Hot Rods have a Clutch!

1955 210 2dr: 327, Brodix IK180 heads, Jones cam, M20, Wilwood front brakes

1982 C-10 SWB pickup, 250 six, 3-speed

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Rick_L 
Honored Member
Posts: 25766

Loc: Katy, Tx, USA
Reg: 07-06-00
07-04-09 07:31 AM - Post#1728900    
    In response to MikeB

You need some sort of residual valve with a drum brake.

There are two versions of the brass bodied combination valve pictured. One is for disc/drum, and it has a residual valve in the port for the rear (drum) brakes. The other is for disc/disc, and it doesn't have the residual valve.

The light (2 psi) valves are for when the m/c is below the calipers or wheel cylinders, like on a street rod or an older car or truck where the pedal goes through the floor instead of hanging like on 55-57s.

I think that no matter how well you attempt to match the front and rear brakes, you're just lucky if you don't need a proportining valve. There are a lot of variables.

 
52chevybob 
Dedicated Enthusiast
Posts: 5628

Reg: 05-27-08
07-04-09 02:08 PM - Post#1729116    
    In response to Rick_L

I'm of the no residual valve camp wiht MCs on the firewall. The shoes on drum brakes should go all the way to the stops to maintain a good brake feel, the pedal always stopping at the same point. Disc brakes don't want a residual valve unless necessary to keep fluid in the wheel. The pad for the disc needs to be pushed back in with low pressure or the pad gets worn more frp, tje draggomg die tp the residual pressure in the brake. Basically, the only thing that I really see with residual valves is that they keep the brakes engaged at all times, reducing gas milage and shortening brake life.

 
MikeB 
Senior Member
Posts: 9479
MikeB
Loc: Plano, TX
Reg: 08-28-03
07-04-09 03:25 PM - Post#1729163    
    In response to 52chevybob

Bob, I doubt 10 psi pushing against the rear drum springs will keep the brakes engaged.

Here's an excerpt from an article by Dean Oshiro at Hot Rods USA:

Residual valves are pressure valves used to retain pressure in the lines. The most common use is on a hot rod when there is a floor mounted brake pedal and master cylinder. Mounting the master cylinder (M/C) below the floor positions it below the calipers. Gravity will cause the fluid to flow away from the calipers. The residual valve will retain pressure within the lines. (i.e. 2 pounds residual valve will retain 2 pounds of pressure, 10 pound will retain 10 pounds.) Drum brake master cylinders have residual valve(s) built into the master cylinder. This is needed to maintain pressure against the cup seals in the wheel cylinders. If you are using a disc brake master cylinder or after market you will need to install a 10 pound residual valve for the drum brakes. Do not install a residual valve if your master cylinder already has one in it. This will cause the brakes to lock up after the second application to the brake pedal.

Distribution Blocks or Combination Valves: One of the biggest misconceptions is the distribution block or combination valve. Almost every factory car has one. This usually serves as a metering block to adjust the proportioning to the rear brakes, as a "T" fitting for your front left and right front brake lines and brake light warning switch. What people fail to understand is that each car is "engineered" for a specific distribution block based on weight, braking characteristics and tires. So generally most factory cars have different blocks.

Ask yourself this. How can one distribution block be engineered for all applications? So, we have this 23T with tiny tires in front and big tires in the back, we have a 57 Caddy and a 57 Chevy pick up. Do you really think the braking is the same for all three vehicles?

Save yourself some headaches install a adjustable proportional valve in the rear brake lines.

Copyright reserved by Dean Oshiro.

Real Hot Rods have a Clutch!

1955 210 2dr: 327, Brodix IK180 heads, Jones cam, M20, Wilwood front brakes

1982 C-10 SWB pickup, 250 six, 3-speed

My car pictures



Edited by MikeB on 07-04-09 03:26 PM. Reason for edit: No reason given.

 
Rick_L 
Honored Member
Posts: 25766

Loc: Katy, Tx, USA
Reg: 07-06-00
07-04-09 03:30 PM - Post#1729166    
    In response to MikeB

Chevy and the rest of the manufacturers used residual valves in the drum brake lines from forever. In the early years they were in the master cylinder outlet port. Then with the advent of front disc/rear drum they moved the residual valve to the combination valve.

You should run them too, whether the brakes are stock or modified. They did it for a reason - they would not have added that cost however small unless it was needed.

Only the unknowing or hardheaded deny the use of these. And some of the unknowing have them and don't realize they do.

 
CJS57 
Frequent Contributor
Posts: 2462
CJS57
Age: 68
Loc: New Milford , Connecticut
Reg: 01-18-05
07-04-09 06:02 PM - Post#1729223    
    In response to Rick_L

I have a little practical experience with 10 lb. residual valves. I removed mine from my stock MC. I then adjusted the rear brake shoes real tight to the drums. The brake pedal feel was perfect, high and hard. After a few miles, the rear brakes wore in, and the pedal feel changed, not quite as good. Not as high, not as hard. This is where the residual presure valve comes in. It keeps the pedal feel high and hard as the drum brakes wear in. Hope this helps! Chris
1957 Belair 2Dr Hdtp, 58,000 original miles, original never rebuilt 283 engine, 245hp, Dual Fours, Tremec TKO 600 5-speed, 3.70 gears, AACA Senior in 1985
previous trifives:
1955 Belair Convt
1956 210 2dr Sdn
1957 Belair 2Dr Hdtp


Edited by CJS57 on 07-04-09 06:03 PM. Reason for edit: No reason given.

 
MikeB 
Senior Member
Posts: 9479
MikeB
Loc: Plano, TX
Reg: 08-28-03
07-05-09 09:24 AM - Post#1729460    
    In response to Rick_L

  • Rick_L Said:
Chevy and the rest of the manufacturers used residual valves in the drum brake lines from forever.


What's your opinion on a 2 psi valve for front discs? I plan to do some line re-rotuing this fall, and wonder if I should install one.
Real Hot Rods have a Clutch!

1955 210 2dr: 327, Brodix IK180 heads, Jones cam, M20, Wilwood front brakes

1982 C-10 SWB pickup, 250 six, 3-speed

My car pictures



 
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